I will be building my first new pc in several years soon and I am very interested in the possibility of running two instances of a game and letting a friend join me. Is that possible? It will be a very powerful pc, I'm not concerned about having the processing power or memory to do it. I am assuming the worst I'll have to do from that standpoint is buy an additional video card or settle some kind of network conflict.
My real concern is two sets of keyboads and mice controlling two different environments. The only time I have experienced such a thing was remoting into a server and that had very crappy video. Not to mention this isn't remote. I plan on using long cables in the walls and using the two 55" LEDs I have in the living room
(I have no clue if that last part matters but if someone is going to be nice enough to help me I don't want to surprise you at the end by saying I will not be in the room with the PC tower.)
Well the real problem you will have will not be the CPU power to run two games at once but even if you could get two instances of the same game running at once (and most games will not let you do that) the game will default the the primary graphics card for both games and that will probably not work well. As far a the 55" TV that should be no problem as 1080p is 1080p whether it is from a 27" monitor or a 55" tv.
The length of the HDMI I do not know about I have never tried to run one that long before but I would hazard to guess that you may need a signal booster for one that long.
http://www.miniframe.com/ has one way to do it, essentially it splits different user accounts over multiple monitors with separate keyboards and mice. There are other ways to do it with virtualization, but if you want to keep it to a single OS, softXpand is probably your safest bet.
This guy has clearly also never heard of sandboxie, which allows you to run multiple instances of the same application where you would normally be restricted, by creating temporary partitions of your hard drive. Combined with Softxpand, this is a pretty robust solution.
Also, USB certainly works over 25m (approximately 75'), so the part about your keyboards and mice not working is just plain wrong - they will. I don't know about HDMI though, never tried running one that long... DVI will I think though and that's electrically the same so you could be ok...
I know this is an old thread now but I just thought some accuracy and helpfulness rather than just suggesting a less efficient solution would be appreciated. I myself run 4 users off my PC for LAN parties, since it draws less power that way than 4 separate machines. 4 of us on 1 computer and the other 4 on laptops works a treat.